/*
 * Copyright 2013 The Netty Project
 *
 * The Netty Project licenses this file to you under the Apache License,
 * version 2.0 (the "License"); you may not use this file except in compliance
 * with the License. You may obtain a copy of the License at:
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
 * License for the specific language governing permissions and limitations
 * under the License.
 */
package io.netty.util;

import io.netty.util.internal.StringUtil;
import io.netty.util.internal.logging.InternalLogger;
import io.netty.util.internal.logging.InternalLoggerFactory;

/**
 * Collection of method to handle objects that may implement {@link ReferenceCounted}.
 */
public final class ReferenceCountUtil {

  private static final InternalLogger logger = InternalLoggerFactory
      .getInstance(ReferenceCountUtil.class);

  static {
    ResourceLeakDetector.addExclusions(ReferenceCountUtil.class, "touch");
  }

  /**
   * Try to call {@link ReferenceCounted#retain()} if the specified message implements {@link
   * ReferenceCounted}. If the specified message doesn't implement {@link ReferenceCounted}, this
   * method does nothing.
   */
  @SuppressWarnings("unchecked")
  public static <T> T retain(T msg) {
    if (msg instanceof ReferenceCounted) {
      return (T) ((ReferenceCounted) msg).retain();
    }
    return msg;
  }

  /**
   * Try to call {@link ReferenceCounted#retain(int)} if the specified message implements {@link
   * ReferenceCounted}. If the specified message doesn't implement {@link ReferenceCounted}, this
   * method does nothing.
   */
  @SuppressWarnings("unchecked")
  public static <T> T retain(T msg, int increment) {
    if (msg instanceof ReferenceCounted) {
      return (T) ((ReferenceCounted) msg).retain(increment);
    }
    return msg;
  }

  /**
   * Tries to call {@link ReferenceCounted#touch()} if the specified message implements {@link
   * ReferenceCounted}. If the specified message doesn't implement {@link ReferenceCounted}, this
   * method does nothing.
   */
  @SuppressWarnings("unchecked")
  public static <T> T touch(T msg) {
    if (msg instanceof ReferenceCounted) {
      return (T) ((ReferenceCounted) msg).touch();
    }
    return msg;
  }

  /**
   * Tries to call {@link ReferenceCounted#touch(Object)} if the specified message implements {@link
   * ReferenceCounted}.  If the specified message doesn't implement {@link ReferenceCounted}, this
   * method does nothing.
   */
  @SuppressWarnings("unchecked")
  public static <T> T touch(T msg, Object hint) {
    if (msg instanceof ReferenceCounted) {
      return (T) ((ReferenceCounted) msg).touch(hint);
    }
    return msg;
  }

  /**
   * Try to call {@link ReferenceCounted#release()} if the specified message implements {@link
   * ReferenceCounted}. If the specified message doesn't implement {@link ReferenceCounted}, this
   * method does nothing.
   */
  public static boolean release(Object msg) {
    if (msg instanceof ReferenceCounted) {
      return ((ReferenceCounted) msg).release();
    }
    return false;
  }

  /**
   * Try to call {@link ReferenceCounted#release(int)} if the specified message implements {@link
   * ReferenceCounted}. If the specified message doesn't implement {@link ReferenceCounted}, this
   * method does nothing.
   */
  public static boolean release(Object msg, int decrement) {
    if (msg instanceof ReferenceCounted) {
      return ((ReferenceCounted) msg).release(decrement);
    }
    return false;
  }

  /**
   * Try to call {@link ReferenceCounted#release()} if the specified message implements {@link
   * ReferenceCounted}. If the specified message doesn't implement {@link ReferenceCounted}, this
   * method does nothing. Unlike {@link #release(Object)} this method catches an exception raised by
   * {@link ReferenceCounted#release()} and logs it, rather than rethrowing it to the caller.  It is
   * usually recommended to use {@link #release(Object)} instead, unless you absolutely need to
   * swallow an exception.
   */
  public static void safeRelease(Object msg) {
    try {
      release(msg);
    } catch (Throwable t) {
      logger.warn("Failed to release a message: {}", msg, t);
    }
  }

  /**
   * Try to call {@link ReferenceCounted#release(int)} if the specified message implements {@link
   * ReferenceCounted}. If the specified message doesn't implement {@link ReferenceCounted}, this
   * method does nothing. Unlike {@link #release(Object)} this method catches an exception raised by
   * {@link ReferenceCounted#release(int)} and logs it, rather than rethrowing it to the caller.  It
   * is usually recommended to use {@link #release(Object, int)} instead, unless you absolutely need
   * to swallow an exception.
   */
  public static void safeRelease(Object msg, int decrement) {
    try {
      release(msg, decrement);
    } catch (Throwable t) {
      if (logger.isWarnEnabled()) {
        logger.warn("Failed to release a message: {} (decrement: {})", msg, decrement, t);
      }
    }
  }

  /**
   * Schedules the specified object to be released when the caller thread terminates. Note that this
   * operation is intended to simplify reference counting of ephemeral objects during unit tests. Do
   * not use it beyond the intended use case.
   *
   * @deprecated this may introduce a lot of memory usage so it is generally preferable to manually
   * release objects.
   */
  @Deprecated
  public static <T> T releaseLater(T msg) {
    return releaseLater(msg, 1);
  }

  /**
   * Schedules the specified object to be released when the caller thread terminates. Note that this
   * operation is intended to simplify reference counting of ephemeral objects during unit tests. Do
   * not use it beyond the intended use case.
   *
   * @deprecated this may introduce a lot of memory usage so it is generally preferable to manually
   * release objects.
   */
  @Deprecated
  public static <T> T releaseLater(T msg, int decrement) {
    if (msg instanceof ReferenceCounted) {
      ThreadDeathWatcher
          .watch(Thread.currentThread(), new ReleasingTask((ReferenceCounted) msg, decrement));
    }
    return msg;
  }

  /**
   * Returns reference count of a {@link ReferenceCounted} object. If object is not type of {@link
   * ReferenceCounted}, {@code -1} is returned.
   */
  public static int refCnt(Object msg) {
    return msg instanceof ReferenceCounted ? ((ReferenceCounted) msg).refCnt() : -1;
  }

  /**
   * Releases the objects when the thread that called {@link #releaseLater(Object)} has been
   * terminated.
   */
  private static final class ReleasingTask implements Runnable {

    private final ReferenceCounted obj;
    private final int decrement;

    ReleasingTask(ReferenceCounted obj, int decrement) {
      this.obj = obj;
      this.decrement = decrement;
    }

    @Override
    public void run() {
      try {
        if (!obj.release(decrement)) {
          logger.warn("Non-zero refCnt: {}", this);
        } else {
          logger.debug("Released: {}", this);
        }
      } catch (Exception ex) {
        logger.warn("Failed to release an object: {}", obj, ex);
      }
    }

    @Override
    public String toString() {
      return StringUtil.simpleClassName(obj) + ".release(" + decrement + ") refCnt: " + obj
          .refCnt();
    }
  }

  private ReferenceCountUtil() {
  }
}
